Conventionally, there is known a sheet finishing apparatus that is arranged at the downstream side of an image forming apparatus such as a copy machine, a printer, a multi-functional peripheral (MFP), or the like and performs post-processes such as sorting, stapling, and the like for a printed sheet.
There are sheet finishing apparatuses of this kind equipped with a fixed tray and a movable tray as trays for discharging and stacking sheets. If a relatively small number of sheets are to be discharged, the fixed tray is usually selected. On the other hand, if a large number of sheets, for example, 1000 or more sheets are to be discharged, the movable tray is selected. In addition, if sorting or stapling is to be performed for a sheet bundle, the movable tray is also selected.
The movable tray is configured to move up and down along an external wall of the main body of the e according to the number of sheets in order to stack a large number of sheets. If the number of sheets is small, the movable tray receives sheets at a high position, and the tray is lowered as the number of sheets becomes larger.
A stacking surface of the movable tray is inclined at a predetermined inclination angle so that the leading end of a sheet is positioned higher than the trailing end thereof. The inclination of the stacking surface of the movable tray prevents stacked sheets from falling out of the movable tray. The trailing end of a sheet slipping down along the inclination of the stacking surface comes into contact with the external wall of the main body of the sheet finishing apparatus and stops.
If the number of sheets stacked on the movable tray is large, the pressure with which the trailing ends of the sheets press against the external wall becomes high, thereby generating friction between the trailing ends of the sheets and the external wall. For this reason, when the movable tray moves up and down, unpleasant abnormal noise (friction noise) occurs between the trailing ends of sheets stacked on the movable tray and the external wall.
For this reason, there is demand for a sheet finishing apparatus which can reduce friction between the trailing ends of stacked sheets and the external wall of the main body of the sheet finishing apparatus and suppress the generation of abnormal noise.